The present invention relates to aromatics alkylation, and in particular to the alkylation of benzene with ethylene and propylene to produce ethylbenzene and cumene, respectively. In addition, the invention is concerned with the alkylation of aromatics with long chain (C6+) alkylating agents to produce long chain alkylbenzenes.
Ethylbenzene and cumene are valuable commodity chemicals which are used industrially for the production of styrene monomer and phenol, respectively. In addition, long chain alkylbenzenes are useful as lubricant base stocks and as intermediates in the production of detergents.
Alkylation is one of the most important and useful reactions of hydrocarbons. Lewis and Bronsted acids, including a variety of natural and synthetic zeolites, have been used as alkylation catalysts. Alkylation of aromatic hydrocarbon compounds employing certain crystalline zeolite catalysts is known in the art. In particular, alkylation of benzene with ethylene and propylene in the presence of zeolite catalysts represents the preferred commercial techniques for the production of ethylbenzene and cumene.
For example, U.S. Pat. No. 4,992,606 describes the use of MCM-22 in the alkylation of aromatic compounds, such as benzene, with alkylating agents having aliphatic groups with 1 to 5 carbon atoms, such as ethylene and propylene. Similarly, U.S. Pat. No. 4,962,256 describes the use of MCM-22 in the alkylation of aromatic compounds with alkylating agents having aliphatic groups with at least 6 carbon atoms.
The use of MCM-49 in the alkylation of aromatic compounds with short chain alkylating agents is described in U.S. Pat. No. 5,371,310 and in alkylation of aromatic compounds with long chain alkylating agents is described in U.S. Pat. No. 5,401,896.
The use of MCM-56 in the alkylation of aromatic compounds with short chain alkylating agents is described in U.S. Pat. Nos. 5,453,554 and 5,557,024.
It is also known from U.S. Pat. No. 5,470,810 that the addition of phosphorus to MCM-22 improves the hydrothermal stability of the resulting catalyst for use in catalytic cracking.
U.S. Pat. No. 3,962,364 discloses that the addition of at least 0.5 wt % phosphorus to a zeolite having a constraint index of 1-12, in particular ZSM-5, increases the selectivity of the zeolite in the vapor phase alkylation of aromatic hydrocarbons with olefins.
According to the invention, it has now been found that modification of MCM-22 and certain related molecular sieve catalysts, such as MCM-49 and MCM-56, with phosphorus increases the activity of the catalyst for the alkylation of aromatic compounds. In addition, the phosphorus modification increases the selectivity of the catalyst towards the monoalkylated product and enhances its stability against the hydrothermal deactivation which can occur during regeneration.